LVM and multiple iSCSI disks performance of LVM

xxx_anuj_xxx · 04-29-2008, 07:57 AM

Hi,
I have a LVM performance related question.
Issue:
We have multiple iscsi-target machines say iscsi-target1, iscsi-target2, iscsi-target3, iscsi-target4,....iscsi-targetN imported on iSCSI-initiator Machine (FileServer).

I used lvm and created a logical volume say MyBigStorage on FileServer using /dev/sda1, /dev/sda2, /dev/sda3..../dev/sdaN as physical disks (these are the raw disks exported from iscsi-target machines).

Question:
1. Is it going to take more time if a client machine looks for a file which is on FileServer's LVM MyBigStorage, as my LVM is created using multiple raw disks using iscsi-targets.

2. What would be impact over performance (file lookup) in case we increase more iscsi-target machines, and expand our MyBigStorage lvm using newly attached iscsi-target disks?

3. The file system we are going to use is GFS or ext3 and the overall data is between 4TB to 8TB.

4. Any other issue which you can suggest with above approach?

Thanks and Regards
Anuj Singh.

frndrfoe · 04-29-2008, 09:22 AM

I have a system hosting about 11 TB from 5 iscsi attached disk appliances and we see no file access problems.
Things to consider:
1. Dedicated gig or better switch/network to connect head unit to wherever the disks live.
2. CLVM - if using multiple heads. I am assuming multiple heads if considering GFS.
3. We had bad luck with GFS, file locking mechanism lost it's brains from time to time, now we are happily using ext3. It was a pain and disruptive to have to take down the high availability cluster so that we could restart GFS. It wasn't very "high availability"

xxx_anuj_xxx · 04-30-2008, 12:01 AM

Hi,
Which version of GFS you tried?
Which file locking are you using with your ext3 & which you used with GFS?

Thanks and regards
Anuj Singh

xxx_anuj_xxx · 05-01-2008, 01:13 AM

Hi frndrfoe,
afaik ext3 is not cluster aware file system, what mechanism are you using to prevent data corruption?
thanks and regards
Anuj Singh.

frndrfoe · 05-01-2008, 12:26 PM

we just have a two node failover system so only one node serves any one filesystem at a time so its working for our unique situation.

We are moving to Netapp this summer so we are just sticking it out.